swift - Positioning spinner within UIAlertController -

i have uialertcontroller title , spinner. need spinner displayed below title, i'm struggling position it. in fact, i'm setting spinner.center center of screen, it's appearing in lower right hand corner.

var alert: uialertcontroller = uialertcontroller(title: "fetching new music", message: nil, preferredstyle: uialertcontrollerstyle.alert)  var spinner: uiactivityindicatorview = uiactivityindicatorview(activityindicatorstyle: uiactivityindicatorviewstyle.whitelarge)  spinner.color = uicolor.yellowcolor()  spinner.startanimating()  alert.view.addsubview(spinner)  var height:nslayoutconstraint = nslayoutconstraint(item: alert.view, attribute: nslayoutattribute.height, relatedby: nslayoutrelation.equal, toitem: nil, attribute: nslayoutattribute.notanattribute, multiplier: 1, constant: self.view.frame.height * 0.15)  alert.view.addconstraint(height)  // here need help!           spinner.center = cgpointmake((self.view.frame.width / 2) - (spinner.frame.width / 2), (self.view.frame.height / 2) - (spinner.frame.height / 2))  self.presentviewcontroller(alert, animated: true, completion: nil) 

these 2 lines, taken together, make no sense:

alert.view.addsubview(spinner) spinner.center = cgpointmake((self.view.frame.width / 2) - (spinner.frame.width / 2), (self.view.frame.height / 2) - (spinner.frame.height / 2)) 

it appear have not grasped fundamental difference between frame , bounds. if going add spinner subview of alert view (as in first line), position of spinner's center (as in second line) defined in relation the alert view's bounds, not other object's frame.